(a) Field of the Invention
The present invention relates to a method and apparatus for canceling an acoustic echo signal.
(b) Description of the Related Art
An acoustic echo canceller (AEC) is a device that re-inputs an audio signal output from a speaker to a microphone directly or indirectly (through reflection from a wall or a peripheral object) in a video call, a video conference, or the like, to thus cancel acoustic echo, which is the repetition of a sound of a user. In canceling acoustic echo with an AEC, it is very important to accurately estimate an acoustic echo generation path (or a room impulse response (RIR)). In general, the AEC estimates the acoustic echo generation path (or RIR) by using an adaptive filter, and generates an estimated acoustic echo signal. Thereafter, the AEC subtracts the estimated acoustic echo signal from an actual acoustic echo signal, thus canceling acoustic echo.
A method of updating an adaptive filter coefficient of an adaptive filter for estimating an acoustic echo generation path (or RIR) includes a method of using a recursive least squares (RLS) algorithm, a method of using a least mean square (LMS) algorithm, a method of using a normalized least mean square (NLMS) algorithm, a method of using an affine projection algorithm, and the like. Each updating method is implemented even in a frequency domain and a sub-band domain, as well as in a time domain. Most AECs use the NLMS algorithm due to a small amount of calculation and ease in implementation. Meanwhile, in a case of updating an adaptive filter coefficient, the NLMS algorithm requires a step size parameter. If a step size is large, an acoustic echo generation path may be more promptly estimated, but a difference between the estimated acoustic echo generation path and an actual acoustic echo generation path is increased. Conversely, if a step size is small, an acoustic echo generation path may be more accurately estimated, but more time is required for estimation. Thus, in order to enhance both a convergence speed as to how fast an estimated acoustic echo generation path is converged on an actual acoustic echo generation path and accuracy of the estimated acoustic echo signal, a step size is required to be variably controlled. Various methods of variably controlling a step size have been proposed.
Recently, Qualcomm has proposed a method of adjusting a step size resistant to double torque by estimating energy of a noise signal and an audio signal of a near-end talker signal in a time domain through U.S. Patent Laid-Open Publication No. 2010/0057454. Meanwhile, Yin Zhou and Xiaodong Li presented a method of controlling a step size in a frequency domain such that increments of errors (adaptive filter mismatch errors) between an adaptive filter coefficient and an actual acoustic echo generation path are minimized, in an article entitled “A variable step-size for frequency-domain acoustic echo cancellation”.
However, the foregoing related arts have a problem in that, when an actual acoustic echo generation path is changed over time, an adaptive filter coefficient cannot quickly follow the actual acoustic echo generation path in a frequency domain.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.